For many food products, especially prepackaged sandwiches, moisture levels must be maintained if the product is to exhibit optimum organoleptic properties, quality, and taste. Moisture migration in finished food products can seriously compromise quality, stability, and organoleptic properties. In addition, many chemical and enzymatic deteriorative reactions proceed at rates partially governed by the moisture content of foods. Excessive rates of these reactions can promote deleterious changes in the flavor, color, texture, and nutritive value of food products.
In multi-component food products, particularly those having components with different moisture contents and water activities such as prepackaged grilled cheese sandwiches, moisture can migrate between adjacent components, altering the component's characteristics and organoleptic properties. In addition to compromising the quality of finished food products, moisture migration can hinder production and distribution of food products. Thus, for example, the cheese in the sandwich may dry out while, at the same time, the texture of the bread may change with time, especially becoming soft and/or soggy.
One method to prevent moisture migration in foods involves coating one or more surfaces of the food product with an edible moisture barrier. Such barriers should have a low moisture permeability in order to prevent the migration of water between areas of differing water activities. In addition, the barrier should cover the food surface completely, including crevices, and adhere well to the food product surface. The moisture barrier should be sufficiently strong, soft, and flexible to form a continuous surface that will not crack upon handling, yet can be easily penetrated during consumption. In addition, the barrier film's organoleptic properties of taste, aftertaste, and mouthfeel should be imperceptible so that the consumer is not aware of the barrier when the food product is consumed. Finally, the moisture barrier should be easy to manufacture and easy to use.
Because lipids, such as oils, fats, and waxes, are composed of lipophilic water insoluble molecules capable of forming a water impervious structure, they have been investigated for use in moisture barrier films. With respect to oleaginous materials derived from lipids (i.e., sucrose polyesters, acetylated monoglycerides and the like) and/or other film forming lipids, it has been shown that, unless an undesirably thick coating is used, the barrier is not sufficiently effective for food products requiring long shelf life. Such film forming lipids tend to become unstable under normal, practical use condition and lose film integrity and barrier effectiveness. In addition to structural instability, such as oiling out or cracking upon handling or with changes in temperatures, such lipid-based moisture barriers have disadvantages of being organoleptically unacceptable (greasy or waxy mouthfeel).
Accordingly, many of the barriers in the art use a water-impermeable lipid in association with hydrocolloids or polysaccharides such as alginate, pectin, carrageenan, cellulose derivatives, starch, starch hydrolysates, and/or gelatin to form gel structures or crosslinked semi-rigid matrixes to entrap and/or immobilize the nonaqueous or lipid material. In many cases these components are formed as bilayer films. These bilayer films may be precast and applied to a food surface as a self-supporting film with the lipid layer oriented toward the component with highest water activity. See, for example, U.S. Pat. No. 4,671,963 (Jun. 9, 1987), U.S. Pat. No. 4,880,646 (Nov. 14, 1987), U.S. Pat. No. 4,915,971 (Apr. 10, 1990), and U.S. Pat. No. 5,130,151 (Jul. 14, 1992). There are, however, a number of drawbacks associated with these moisture barriers. The hydrocolloids themselves are hydrophilic and/or water soluble and thus tend to absorb water with time. The absorption of water by the hydrophilic material in moisture barrier is greatly accelerated while the film is directly in contact with foods having a water activity (Aw) above 0.75. In addition, some hydrocolloids tend to make the barriers fairly stiff, requiring the addition of a hydrophilic plasticizer (e.g., polyol) to increase flexibility. These plasticizers are often strong moisture binder themselves thus promoting moisture migration into the barriers and decreased structural stability and effectiveness of the barriers. Furthermore, the texture and the required thickness of some of these barriers may make their presence perceptible and objectionable when the product is consumed. Additional processing steps (casting and drying) required to form these films make them difficult to use in high speed commercial production.
In the case of prepackaged grilled cheese sandwiches, a fat barrier is typically applied to the side of the bread facing the cheese, as described in U.S. Pat. No. 6,139,885. Moisture from the cheese can be transmitted through the air around the barrier to other parts of the bread, rendering the bread soggy. Even if sealing the part of the toast in contact with the cheese were sufficient to prevent moisture migration, the bread/toast has many nooks and crannies, making effective sealing of the surface for the purpose of moisture barrier extremely difficult under refrigerated conditions without an extremely thick coating of the barrier material. Thick coatings tend to be unpalatable to most consumers.
A particular type of barrier as described in U.S. Pat. No. 6,139,885 yields a more static layer that tends to remain in place to a greater extent after the cheese has melted. Hence, this type of barrier is more noticeable to the consumer. Application of the barrier to the toast results in a product that has a more noticeable barrier since the cheese does not flow next to it.